2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
34 #include "ucioption.h"
40 Key Position::zobrist[2][8][64];
41 Key Position::zobEp[64];
42 Key Position::zobCastle[16];
43 Key Position::zobSideToMove;
44 Key Position::zobExclusion;
46 Score Position::PieceSquareTable[16][64];
48 // Material values arrays, indexed by Piece
49 const Value Position::PieceValueMidgame[17] = {
51 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
52 RookValueMidgame, QueenValueMidgame, VALUE_ZERO,
53 VALUE_ZERO, VALUE_ZERO,
54 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
55 RookValueMidgame, QueenValueMidgame
58 const Value Position::PieceValueEndgame[17] = {
60 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
61 RookValueEndgame, QueenValueEndgame, VALUE_ZERO,
62 VALUE_ZERO, VALUE_ZERO,
63 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
64 RookValueEndgame, QueenValueEndgame
67 // Material values array used by SEE, indexed by PieceType
68 const Value Position::seeValues[] = {
70 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
71 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10
77 // Bonus for having the side to move (modified by Joona Kiiski)
78 const Score TempoValue = make_score(48, 22);
80 struct PieceLetters : public std::map<char, Piece> {
84 operator[]('K') = WK; operator[]('k') = BK;
85 operator[]('Q') = WQ; operator[]('q') = BQ;
86 operator[]('R') = WR; operator[]('r') = BR;
87 operator[]('B') = WB; operator[]('b') = BB;
88 operator[]('N') = WN; operator[]('n') = BN;
89 operator[]('P') = WP; operator[]('p') = BP;
90 operator[](' ') = PIECE_NONE;
91 operator[]('.') = PIECE_NONE_DARK_SQ;
94 char from_piece(Piece p) const {
96 std::map<char, Piece>::const_iterator it;
97 for (it = begin(); it != end(); ++it)
106 PieceLetters pieceLetters;
112 CheckInfo::CheckInfo(const Position& pos) {
114 Color us = pos.side_to_move();
115 Color them = opposite_color(us);
117 ksq = pos.king_square(them);
118 dcCandidates = pos.discovered_check_candidates(us);
120 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
121 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
122 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
123 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
124 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
125 checkSq[KING] = EmptyBoardBB;
129 /// Position c'tors. Here we always create a copy of the original position
130 /// or the FEN string, we want the new born Position object do not depend
131 /// on any external data so we detach state pointer from the source one.
133 Position::Position(const Position& pos, int th) {
135 memcpy(this, &pos, sizeof(Position));
136 detach(); // Always detach() in copy c'tor to avoid surprises
141 Position::Position(const string& fen, bool isChess960, int th) {
143 from_fen(fen, isChess960);
148 /// Position::detach() copies the content of the current state and castling
149 /// masks inside the position itself. This is needed when the st pointee could
150 /// become stale, as example because the caller is about to going out of scope.
152 void Position::detach() {
156 st->previous = NULL; // as a safe guard
160 /// Position::from_fen() initializes the position object with the given FEN
161 /// string. This function is not very robust - make sure that input FENs are
162 /// correct (this is assumed to be the responsibility of the GUI).
164 void Position::from_fen(const string& fen, bool isChess960) {
166 A FEN string defines a particular position using only the ASCII character set.
168 A FEN string contains six fields. The separator between fields is a space. The fields are:
170 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
171 with rank 1; within each rank, the contents of each square are described from file A through file H.
172 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
173 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
174 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
175 of blank squares), and "/" separate ranks.
177 2) Active color. "w" means white moves next, "b" means black.
179 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
180 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
181 kingside), and/or "q" (Black can castle queenside).
183 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
184 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
185 regardless of whether there is a pawn in position to make an en passant capture.
187 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
188 to determine if a draw can be claimed under the fifty-move rule.
190 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
195 std::istringstream ss(fen);
200 // 1. Piece placement field
201 while (ss.get(token) && token != ' ')
203 if (pieceLetters.find(token) != pieceLetters.end())
205 put_piece(pieceLetters[token], sq);
208 else if (isdigit(token))
209 sq += Square(token - '0'); // Skip the given number of files
210 else if (token == '/')
211 sq -= SQ_A3; // Jump back of 2 rows
217 if (!ss.get(token) || (token != 'w' && token != 'b'))
220 sideToMove = (token == 'w' ? WHITE : BLACK);
222 if (!ss.get(token) || token != ' ')
225 // 3. Castling availability
226 while (ss.get(token) && token != ' ')
227 if (!set_castling_rights(token))
230 // 4. En passant square
232 if ( (ss.get(col) && (col >= 'a' && col <= 'h'))
233 && (ss.get(row) && (row == '3' || row == '6')))
235 st->epSquare = make_square(file_from_char(col), rank_from_char(row));
237 // Ignore if no capture is possible
238 Color them = opposite_color(sideToMove);
239 if (!(attacks_from<PAWN>(st->epSquare, them) & pieces(PAWN, sideToMove)))
240 st->epSquare = SQ_NONE;
247 // 6. Fullmove number
249 startPosPlyCounter = (fmn - 1) * 2 + int(sideToMove == BLACK);
251 // Various initialisations
252 castleRightsMask[make_square(initialKFile, RANK_1)] ^= WHITE_OO | WHITE_OOO;
253 castleRightsMask[make_square(initialKFile, RANK_8)] ^= BLACK_OO | BLACK_OOO;
254 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
255 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
256 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
257 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
259 chess960 = isChess960;
262 st->key = compute_key();
263 st->pawnKey = compute_pawn_key();
264 st->materialKey = compute_material_key();
265 st->value = compute_value();
266 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
267 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
271 cout << "Error in FEN string: " << fen << endl;
275 /// Position::set_castling_rights() sets castling parameters castling avaiability.
276 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
277 /// that uses the letters of the columns on which the rooks began the game instead
278 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
279 /// associated with the castling right, the traditional castling tag will be replaced
280 /// by the file letter of the involved rook as for the Shredder-FEN.
282 bool Position::set_castling_rights(char token) {
284 Color c = token >= 'a' ? BLACK : WHITE;
285 Square sqA = (c == WHITE ? SQ_A1 : SQ_A8);
286 Square sqH = (c == WHITE ? SQ_H1 : SQ_H8);
287 Piece rook = (c == WHITE ? WR : BR);
289 initialKFile = square_file(king_square(c));
290 token = char(toupper(token));
294 for (Square sq = sqH; sq >= sqA; sq--)
295 if (piece_on(sq) == rook)
298 initialKRFile = square_file(sq);
302 else if (token == 'Q')
304 for (Square sq = sqA; sq <= sqH; sq++)
305 if (piece_on(sq) == rook)
308 initialQRFile = square_file(sq);
312 else if (token >= 'A' && token <= 'H')
314 File rookFile = File(token - 'A') + FILE_A;
315 if (rookFile < initialKFile)
318 initialQRFile = rookFile;
323 initialKRFile = rookFile;
333 /// Position::to_fen() returns a FEN representation of the position. In case
334 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
336 const string Position::to_fen() const {
342 for (Rank rank = RANK_8; rank >= RANK_1; rank--, fen += '/')
344 for (File file = FILE_A; file <= FILE_H; file++)
346 sq = make_square(file, rank);
348 if (square_is_occupied(sq))
355 fen += pieceLetters.from_piece(piece_on(sq));
367 fen += (sideToMove == WHITE ? " w " : " b ");
369 if (st->castleRights != CASTLES_NONE)
371 if (can_castle_kingside(WHITE))
372 fen += chess960 ? char(toupper(file_to_char(initialKRFile))) : 'K';
374 if (can_castle_queenside(WHITE))
375 fen += chess960 ? char(toupper(file_to_char(initialQRFile))) : 'Q';
377 if (can_castle_kingside(BLACK))
378 fen += chess960 ? file_to_char(initialKRFile) : 'k';
380 if (can_castle_queenside(BLACK))
381 fen += chess960 ? file_to_char(initialQRFile) : 'q';
385 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
390 /// Position::print() prints an ASCII representation of the position to
391 /// the standard output. If a move is given then also the san is printed.
393 void Position::print(Move move) const {
395 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
399 Position p(*this, thread());
400 string dd = (color_of_piece_on(move_from(move)) == BLACK ? ".." : "");
401 cout << "\nMove is: " << dd << move_to_san(p, move);
404 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
406 cout << dottedLine << '|';
407 for (File file = FILE_A; file <= FILE_H; file++)
409 Square sq = make_square(file, rank);
410 Piece piece = piece_on(sq);
412 if (piece == PIECE_NONE && square_color(sq) == DARK)
413 piece = PIECE_NONE_DARK_SQ;
415 char c = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
416 cout << c << pieceLetters.from_piece(piece) << c << '|';
419 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
423 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
424 /// king) pieces for the given color and for the given pinner type. Or, when
425 /// template parameter FindPinned is false, the pieces of the given color
426 /// candidate for a discovery check against the enemy king.
427 /// Bitboard checkersBB must be already updated when looking for pinners.
429 template<bool FindPinned>
430 Bitboard Position::hidden_checkers(Color c) const {
432 Bitboard result = EmptyBoardBB;
433 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
435 // Pinned pieces protect our king, dicovery checks attack
437 Square ksq = king_square(FindPinned ? c : opposite_color(c));
439 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
440 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
442 if (FindPinned && pinners)
443 pinners &= ~st->checkersBB;
447 Square s = pop_1st_bit(&pinners);
448 Bitboard b = squares_between(s, ksq) & occupied_squares();
452 if ( !(b & (b - 1)) // Only one bit set?
453 && (b & pieces_of_color(c))) // Is an our piece?
460 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
461 /// king) pieces for the given color. Note that checkersBB bitboard must
462 /// be already updated.
464 Bitboard Position::pinned_pieces(Color c) const {
466 return hidden_checkers<true>(c);
470 /// Position:discovered_check_candidates() returns a bitboard containing all
471 /// pieces for the given side which are candidates for giving a discovered
472 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
473 /// to be already updated.
475 Bitboard Position::discovered_check_candidates(Color c) const {
477 return hidden_checkers<false>(c);
480 /// Position::attackers_to() computes a bitboard containing all pieces which
481 /// attacks a given square.
483 Bitboard Position::attackers_to(Square s) const {
485 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
486 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
487 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
488 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
489 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
490 | (attacks_from<KING>(s) & pieces(KING));
493 /// Position::attacks_from() computes a bitboard of all attacks
494 /// of a given piece put in a given square.
496 Bitboard Position::attacks_from(Piece p, Square s) const {
498 assert(square_is_ok(s));
502 case WB: case BB: return attacks_from<BISHOP>(s);
503 case WR: case BR: return attacks_from<ROOK>(s);
504 case WQ: case BQ: return attacks_from<QUEEN>(s);
505 default: return StepAttacksBB[p][s];
509 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
511 assert(square_is_ok(s));
515 case WB: case BB: return bishop_attacks_bb(s, occ);
516 case WR: case BR: return rook_attacks_bb(s, occ);
517 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
518 default: return StepAttacksBB[p][s];
523 /// Position::move_attacks_square() tests whether a move from the current
524 /// position attacks a given square.
526 bool Position::move_attacks_square(Move m, Square s) const {
528 assert(move_is_ok(m));
529 assert(square_is_ok(s));
532 Square f = move_from(m), t = move_to(m);
534 assert(square_is_occupied(f));
536 if (bit_is_set(attacks_from(piece_on(f), t), s))
539 // Move the piece and scan for X-ray attacks behind it
540 occ = occupied_squares();
541 do_move_bb(&occ, make_move_bb(f, t));
542 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
543 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
544 & pieces_of_color(color_of_piece_on(f));
546 // If we have attacks we need to verify that are caused by our move
547 // and are not already existent ones.
548 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
552 /// Position::find_checkers() computes the checkersBB bitboard, which
553 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
554 /// currently works by calling Position::attackers_to, which is probably
555 /// inefficient. Consider rewriting this function to use the last move
556 /// played, like in non-bitboard versions of Glaurung.
558 void Position::find_checkers() {
560 Color us = side_to_move();
561 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
565 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
567 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
570 assert(move_is_ok(m));
571 assert(pinned == pinned_pieces(side_to_move()));
573 // Castling moves are checked for legality during move generation.
574 if (move_is_castle(m))
577 // En passant captures are a tricky special case. Because they are
578 // rather uncommon, we do it simply by testing whether the king is attacked
579 // after the move is made
582 Color us = side_to_move();
583 Color them = opposite_color(us);
584 Square from = move_from(m);
585 Square to = move_to(m);
586 Square capsq = make_square(square_file(to), square_rank(from));
587 Square ksq = king_square(us);
588 Bitboard b = occupied_squares();
590 assert(to == ep_square());
591 assert(piece_on(from) == make_piece(us, PAWN));
592 assert(piece_on(capsq) == make_piece(them, PAWN));
593 assert(piece_on(to) == PIECE_NONE);
596 clear_bit(&b, capsq);
599 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
600 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
603 Color us = side_to_move();
604 Square from = move_from(m);
606 assert(color_of_piece_on(from) == us);
607 assert(piece_on(king_square(us)) == make_piece(us, KING));
609 // If the moving piece is a king, check whether the destination
610 // square is attacked by the opponent.
611 if (type_of_piece_on(from) == KING)
612 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
614 // A non-king move is legal if and only if it is not pinned or it
615 // is moving along the ray towards or away from the king.
617 || !bit_is_set(pinned, from)
618 || squares_aligned(from, move_to(m), king_square(us));
622 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
624 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
628 Color us = side_to_move();
629 Square from = move_from(m);
630 Square to = move_to(m);
632 // King moves and en-passant captures are verified in pl_move_is_legal()
633 if (type_of_piece_on(from) == KING || move_is_ep(m))
634 return pl_move_is_legal(m, pinned);
636 Bitboard target = checkers();
637 Square checksq = pop_1st_bit(&target);
639 if (target) // double check ?
642 // Our move must be a blocking evasion or a capture of the checking piece
643 target = squares_between(checksq, king_square(us)) | checkers();
644 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
647 /// Position::move_is_legal() takes a position and a (not necessarily pseudo-legal)
648 /// move and tests whether the move is legal. This version is not very fast and
649 /// should be used only in non time-critical paths.
651 bool Position::move_is_legal(const Move m) const {
653 MoveStack mlist[MAX_MOVES];
654 MoveStack *cur, *last = generate<MV_PSEUDO_LEGAL>(*this, mlist);
656 for (cur = mlist; cur != last; cur++)
658 return pl_move_is_legal(m, pinned_pieces(sideToMove));
664 /// Fast version of Position::move_is_legal() that takes a position a move and
665 /// a bitboard of pinned pieces as input, and tests whether the move is legal.
667 bool Position::move_is_legal(const Move m, Bitboard pinned) const {
670 assert(pinned == pinned_pieces(sideToMove));
672 Color us = sideToMove;
673 Color them = opposite_color(sideToMove);
674 Square from = move_from(m);
675 Square to = move_to(m);
676 Piece pc = piece_on(from);
678 // Use a slower but simpler function for uncommon cases
679 if (move_is_special(m))
680 return move_is_legal(m);
682 // If the from square is not occupied by a piece belonging to the side to
683 // move, the move is obviously not legal.
684 if (color_of_piece(pc) != us)
687 // The destination square cannot be occupied by a friendly piece
688 if (color_of_piece_on(to) == us)
691 // Handle the special case of a pawn move
692 if (type_of_piece(pc) == PAWN)
694 // Move direction must be compatible with pawn color
695 int direction = to - from;
696 if ((us == WHITE) != (direction > 0))
699 // We have already handled promotion moves, so destination
700 // cannot be on the 8/1th rank.
701 if (square_rank(to) == RANK_8 || square_rank(to) == RANK_1)
704 // Proceed according to the square delta between the origin and
705 // destination squares.
712 // Capture. The destination square must be occupied by an enemy
713 // piece (en passant captures was handled earlier).
714 if (color_of_piece_on(to) != them)
720 // Pawn push. The destination square must be empty.
721 if (!square_is_empty(to))
726 // Double white pawn push. The destination square must be on the fourth
727 // rank, and both the destination square and the square between the
728 // source and destination squares must be empty.
729 if ( square_rank(to) != RANK_4
730 || !square_is_empty(to)
731 || !square_is_empty(from + DELTA_N))
736 // Double black pawn push. The destination square must be on the fifth
737 // rank, and both the destination square and the square between the
738 // source and destination squares must be empty.
739 if ( square_rank(to) != RANK_5
740 || !square_is_empty(to)
741 || !square_is_empty(from + DELTA_S))
749 else if (!bit_is_set(attacks_from(pc, from), to))
752 // The move is pseudo-legal, check if it is also legal
753 return in_check() ? pl_move_is_evasion(m, pinned) : pl_move_is_legal(m, pinned);
757 /// Position::move_gives_check() tests whether a pseudo-legal move is a check
759 bool Position::move_gives_check(Move m) const {
761 return move_gives_check(m, CheckInfo(*this));
764 bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
767 assert(move_is_ok(m));
768 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
769 assert(color_of_piece_on(move_from(m)) == side_to_move());
770 assert(piece_on(ci.ksq) == make_piece(opposite_color(side_to_move()), KING));
772 Square from = move_from(m);
773 Square to = move_to(m);
774 PieceType pt = type_of_piece_on(from);
777 if (bit_is_set(ci.checkSq[pt], to))
781 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
783 // For pawn and king moves we need to verify also direction
784 if ( (pt != PAWN && pt != KING)
785 || !squares_aligned(from, to, ci.ksq))
789 // Can we skip the ugly special cases ?
790 if (!move_is_special(m))
793 Color us = side_to_move();
794 Bitboard b = occupied_squares();
796 // Promotion with check ?
797 if (move_is_promotion(m))
801 switch (move_promotion_piece(m))
804 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
806 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
808 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
810 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
816 // En passant capture with check ? We have already handled the case
817 // of direct checks and ordinary discovered check, the only case we
818 // need to handle is the unusual case of a discovered check through
819 // the captured pawn.
822 Square capsq = make_square(square_file(to), square_rank(from));
824 clear_bit(&b, capsq);
826 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
827 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
830 // Castling with check ?
831 if (move_is_castle(m))
833 Square kfrom, kto, rfrom, rto;
839 kto = relative_square(us, SQ_G1);
840 rto = relative_square(us, SQ_F1);
842 kto = relative_square(us, SQ_C1);
843 rto = relative_square(us, SQ_D1);
845 clear_bit(&b, kfrom);
846 clear_bit(&b, rfrom);
849 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
856 /// Position::do_setup_move() makes a permanent move on the board. It should
857 /// be used when setting up a position on board. You can't undo the move.
859 void Position::do_setup_move(Move m) {
865 // Reset "game ply" in case we made a non-reversible move.
866 // "game ply" is used for repetition detection.
870 // Update the number of plies played from the starting position
871 startPosPlyCounter++;
873 // Our StateInfo newSt is about going out of scope so copy
874 // its content before it disappears.
879 /// Position::do_move() makes a move, and saves all information necessary
880 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
881 /// moves should be filtered out before this function is called.
883 void Position::do_move(Move m, StateInfo& newSt) {
886 do_move(m, newSt, ci, move_gives_check(m, ci));
889 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
892 assert(move_is_ok(m));
893 assert(&newSt != st);
898 // Copy some fields of old state to our new StateInfo object except the
899 // ones which are recalculated from scratch anyway, then switch our state
900 // pointer to point to the new, ready to be updated, state.
901 struct ReducedStateInfo {
902 Key pawnKey, materialKey;
903 int castleRights, rule50, gamePly, pliesFromNull;
909 memcpy(&newSt, st, sizeof(ReducedStateInfo));
914 // Save the current key to the history[] array, in order to be able to
915 // detect repetition draws.
916 history[st->gamePly++] = key;
918 // Update side to move
919 key ^= zobSideToMove;
921 // Increment the 50 moves rule draw counter. Resetting it to zero in the
922 // case of non-reversible moves is taken care of later.
926 if (move_is_castle(m))
933 Color us = side_to_move();
934 Color them = opposite_color(us);
935 Square from = move_from(m);
936 Square to = move_to(m);
937 bool ep = move_is_ep(m);
938 bool pm = move_is_promotion(m);
940 Piece piece = piece_on(from);
941 PieceType pt = type_of_piece(piece);
942 PieceType capture = ep ? PAWN : type_of_piece_on(to);
944 assert(color_of_piece_on(from) == us);
945 assert(color_of_piece_on(to) == them || square_is_empty(to));
946 assert(!(ep || pm) || piece == make_piece(us, PAWN));
947 assert(!pm || relative_rank(us, to) == RANK_8);
950 do_capture_move(key, capture, them, to, ep);
953 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
955 // Reset en passant square
956 if (st->epSquare != SQ_NONE)
958 key ^= zobEp[st->epSquare];
959 st->epSquare = SQ_NONE;
962 // Update castle rights, try to shortcut a common case
963 int cm = castleRightsMask[from] & castleRightsMask[to];
964 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
966 key ^= zobCastle[st->castleRights];
967 st->castleRights &= castleRightsMask[from];
968 st->castleRights &= castleRightsMask[to];
969 key ^= zobCastle[st->castleRights];
972 // Prefetch TT access as soon as we know key is updated
973 prefetch((char*)TT.first_entry(key));
976 Bitboard move_bb = make_move_bb(from, to);
977 do_move_bb(&(byColorBB[us]), move_bb);
978 do_move_bb(&(byTypeBB[pt]), move_bb);
979 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
981 board[to] = board[from];
982 board[from] = PIECE_NONE;
984 // Update piece lists, note that index[from] is not updated and
985 // becomes stale. This works as long as index[] is accessed just
986 // by known occupied squares.
987 index[to] = index[from];
988 pieceList[us][pt][index[to]] = to;
990 // If the moving piece was a pawn do some special extra work
993 // Reset rule 50 draw counter
996 // Update pawn hash key and prefetch in L1/L2 cache
997 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
999 // Set en passant square, only if moved pawn can be captured
1000 if ((to ^ from) == 16)
1002 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
1004 st->epSquare = Square((int(from) + int(to)) / 2);
1005 key ^= zobEp[st->epSquare];
1009 if (pm) // promotion ?
1011 PieceType promotion = move_promotion_piece(m);
1013 assert(promotion >= KNIGHT && promotion <= QUEEN);
1015 // Insert promoted piece instead of pawn
1016 clear_bit(&(byTypeBB[PAWN]), to);
1017 set_bit(&(byTypeBB[promotion]), to);
1018 board[to] = make_piece(us, promotion);
1020 // Update piece counts
1021 pieceCount[us][promotion]++;
1022 pieceCount[us][PAWN]--;
1024 // Update material key
1025 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
1026 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
1028 // Update piece lists, move the last pawn at index[to] position
1029 // and shrink the list. Add a new promotion piece to the list.
1030 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
1031 index[lastPawnSquare] = index[to];
1032 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
1033 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
1034 index[to] = pieceCount[us][promotion] - 1;
1035 pieceList[us][promotion][index[to]] = to;
1037 // Partially revert hash keys update
1038 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
1039 st->pawnKey ^= zobrist[us][PAWN][to];
1041 // Partially revert and update incremental scores
1042 st->value -= pst(us, PAWN, to);
1043 st->value += pst(us, promotion, to);
1046 st->npMaterial[us] += PieceValueMidgame[promotion];
1050 // Prefetch pawn and material hash tables
1051 Threads[threadID].pawnTable.prefetch(st->pawnKey);
1052 Threads[threadID].materialTable.prefetch(st->materialKey);
1054 // Update incremental scores
1055 st->value += pst_delta(piece, from, to);
1057 // Set capture piece
1058 st->capturedType = capture;
1060 // Update the key with the final value
1063 // Update checkers bitboard, piece must be already moved
1064 st->checkersBB = EmptyBoardBB;
1069 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1073 if (bit_is_set(ci.checkSq[pt], to))
1074 st->checkersBB = SetMaskBB[to];
1077 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
1080 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
1083 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
1089 sideToMove = opposite_color(sideToMove);
1090 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1096 /// Position::do_capture_move() is a private method used to update captured
1097 /// piece info. It is called from the main Position::do_move function.
1099 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
1101 assert(capture != KING);
1105 // If the captured piece was a pawn, update pawn hash key,
1106 // otherwise update non-pawn material.
1107 if (capture == PAWN)
1109 if (ep) // en passant ?
1111 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
1113 assert(to == st->epSquare);
1114 assert(relative_rank(opposite_color(them), to) == RANK_6);
1115 assert(piece_on(to) == PIECE_NONE);
1116 assert(piece_on(capsq) == make_piece(them, PAWN));
1118 board[capsq] = PIECE_NONE;
1120 st->pawnKey ^= zobrist[them][PAWN][capsq];
1123 st->npMaterial[them] -= PieceValueMidgame[capture];
1125 // Remove captured piece
1126 clear_bit(&(byColorBB[them]), capsq);
1127 clear_bit(&(byTypeBB[capture]), capsq);
1128 clear_bit(&(byTypeBB[0]), capsq);
1131 key ^= zobrist[them][capture][capsq];
1133 // Update incremental scores
1134 st->value -= pst(them, capture, capsq);
1136 // Update piece count
1137 pieceCount[them][capture]--;
1139 // Update material hash key
1140 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1142 // Update piece list, move the last piece at index[capsq] position
1144 // WARNING: This is a not perfectly revresible operation. When we
1145 // will reinsert the captured piece in undo_move() we will put it
1146 // at the end of the list and not in its original place, it means
1147 // index[] and pieceList[] are not guaranteed to be invariant to a
1148 // do_move() + undo_move() sequence.
1149 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1150 index[lastPieceSquare] = index[capsq];
1151 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1152 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1154 // Reset rule 50 counter
1159 /// Position::do_castle_move() is a private method used to make a castling
1160 /// move. It is called from the main Position::do_move function. Note that
1161 /// castling moves are encoded as "king captures friendly rook" moves, for
1162 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1164 void Position::do_castle_move(Move m) {
1166 assert(move_is_ok(m));
1167 assert(move_is_castle(m));
1169 Color us = side_to_move();
1170 Color them = opposite_color(us);
1172 // Reset capture field
1173 st->capturedType = PIECE_TYPE_NONE;
1175 // Find source squares for king and rook
1176 Square kfrom = move_from(m);
1177 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1180 assert(piece_on(kfrom) == make_piece(us, KING));
1181 assert(piece_on(rfrom) == make_piece(us, ROOK));
1183 // Find destination squares for king and rook
1184 if (rfrom > kfrom) // O-O
1186 kto = relative_square(us, SQ_G1);
1187 rto = relative_square(us, SQ_F1);
1189 kto = relative_square(us, SQ_C1);
1190 rto = relative_square(us, SQ_D1);
1193 // Remove pieces from source squares:
1194 clear_bit(&(byColorBB[us]), kfrom);
1195 clear_bit(&(byTypeBB[KING]), kfrom);
1196 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1197 clear_bit(&(byColorBB[us]), rfrom);
1198 clear_bit(&(byTypeBB[ROOK]), rfrom);
1199 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1201 // Put pieces on destination squares:
1202 set_bit(&(byColorBB[us]), kto);
1203 set_bit(&(byTypeBB[KING]), kto);
1204 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1205 set_bit(&(byColorBB[us]), rto);
1206 set_bit(&(byTypeBB[ROOK]), rto);
1207 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1209 // Update board array
1210 Piece king = make_piece(us, KING);
1211 Piece rook = make_piece(us, ROOK);
1212 board[kfrom] = board[rfrom] = PIECE_NONE;
1216 // Update piece lists
1217 pieceList[us][KING][index[kfrom]] = kto;
1218 pieceList[us][ROOK][index[rfrom]] = rto;
1219 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1220 index[kto] = index[kfrom];
1223 // Update incremental scores
1224 st->value += pst_delta(king, kfrom, kto);
1225 st->value += pst_delta(rook, rfrom, rto);
1228 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1229 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1231 // Clear en passant square
1232 if (st->epSquare != SQ_NONE)
1234 st->key ^= zobEp[st->epSquare];
1235 st->epSquare = SQ_NONE;
1238 // Update castling rights
1239 st->key ^= zobCastle[st->castleRights];
1240 st->castleRights &= castleRightsMask[kfrom];
1241 st->key ^= zobCastle[st->castleRights];
1243 // Reset rule 50 counter
1246 // Update checkers BB
1247 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1250 sideToMove = opposite_color(sideToMove);
1251 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1257 /// Position::undo_move() unmakes a move. When it returns, the position should
1258 /// be restored to exactly the same state as before the move was made.
1260 void Position::undo_move(Move m) {
1263 assert(move_is_ok(m));
1265 sideToMove = opposite_color(sideToMove);
1267 if (move_is_castle(m))
1269 undo_castle_move(m);
1273 Color us = side_to_move();
1274 Color them = opposite_color(us);
1275 Square from = move_from(m);
1276 Square to = move_to(m);
1277 bool ep = move_is_ep(m);
1278 bool pm = move_is_promotion(m);
1280 PieceType pt = type_of_piece_on(to);
1282 assert(square_is_empty(from));
1283 assert(color_of_piece_on(to) == us);
1284 assert(!pm || relative_rank(us, to) == RANK_8);
1285 assert(!ep || to == st->previous->epSquare);
1286 assert(!ep || relative_rank(us, to) == RANK_6);
1287 assert(!ep || piece_on(to) == make_piece(us, PAWN));
1289 if (pm) // promotion ?
1291 PieceType promotion = move_promotion_piece(m);
1294 assert(promotion >= KNIGHT && promotion <= QUEEN);
1295 assert(piece_on(to) == make_piece(us, promotion));
1297 // Replace promoted piece with a pawn
1298 clear_bit(&(byTypeBB[promotion]), to);
1299 set_bit(&(byTypeBB[PAWN]), to);
1301 // Update piece counts
1302 pieceCount[us][promotion]--;
1303 pieceCount[us][PAWN]++;
1305 // Update piece list replacing promotion piece with a pawn
1306 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1307 index[lastPromotionSquare] = index[to];
1308 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1309 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1310 index[to] = pieceCount[us][PAWN] - 1;
1311 pieceList[us][PAWN][index[to]] = to;
1314 // Put the piece back at the source square
1315 Bitboard move_bb = make_move_bb(to, from);
1316 do_move_bb(&(byColorBB[us]), move_bb);
1317 do_move_bb(&(byTypeBB[pt]), move_bb);
1318 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1320 board[from] = make_piece(us, pt);
1321 board[to] = PIECE_NONE;
1323 // Update piece list
1324 index[from] = index[to];
1325 pieceList[us][pt][index[from]] = from;
1327 if (st->capturedType)
1332 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1334 assert(st->capturedType != KING);
1335 assert(!ep || square_is_empty(capsq));
1337 // Restore the captured piece
1338 set_bit(&(byColorBB[them]), capsq);
1339 set_bit(&(byTypeBB[st->capturedType]), capsq);
1340 set_bit(&(byTypeBB[0]), capsq);
1342 board[capsq] = make_piece(them, st->capturedType);
1344 // Update piece count
1345 pieceCount[them][st->capturedType]++;
1347 // Update piece list, add a new captured piece in capsq square
1348 index[capsq] = pieceCount[them][st->capturedType] - 1;
1349 pieceList[them][st->capturedType][index[capsq]] = capsq;
1352 // Finally point our state pointer back to the previous state
1359 /// Position::undo_castle_move() is a private method used to unmake a castling
1360 /// move. It is called from the main Position::undo_move function. Note that
1361 /// castling moves are encoded as "king captures friendly rook" moves, for
1362 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1364 void Position::undo_castle_move(Move m) {
1366 assert(move_is_ok(m));
1367 assert(move_is_castle(m));
1369 // When we have arrived here, some work has already been done by
1370 // Position::undo_move. In particular, the side to move has been switched,
1371 // so the code below is correct.
1372 Color us = side_to_move();
1374 // Find source squares for king and rook
1375 Square kfrom = move_from(m);
1376 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1379 // Find destination squares for king and rook
1380 if (rfrom > kfrom) // O-O
1382 kto = relative_square(us, SQ_G1);
1383 rto = relative_square(us, SQ_F1);
1385 kto = relative_square(us, SQ_C1);
1386 rto = relative_square(us, SQ_D1);
1389 assert(piece_on(kto) == make_piece(us, KING));
1390 assert(piece_on(rto) == make_piece(us, ROOK));
1392 // Remove pieces from destination squares:
1393 clear_bit(&(byColorBB[us]), kto);
1394 clear_bit(&(byTypeBB[KING]), kto);
1395 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1396 clear_bit(&(byColorBB[us]), rto);
1397 clear_bit(&(byTypeBB[ROOK]), rto);
1398 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1400 // Put pieces on source squares:
1401 set_bit(&(byColorBB[us]), kfrom);
1402 set_bit(&(byTypeBB[KING]), kfrom);
1403 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1404 set_bit(&(byColorBB[us]), rfrom);
1405 set_bit(&(byTypeBB[ROOK]), rfrom);
1406 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1409 board[rto] = board[kto] = PIECE_NONE;
1410 board[rfrom] = make_piece(us, ROOK);
1411 board[kfrom] = make_piece(us, KING);
1413 // Update piece lists
1414 pieceList[us][KING][index[kto]] = kfrom;
1415 pieceList[us][ROOK][index[rto]] = rfrom;
1416 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1417 index[kfrom] = index[kto];
1420 // Finally point our state pointer back to the previous state
1427 /// Position::do_null_move makes() a "null move": It switches the side to move
1428 /// and updates the hash key without executing any move on the board.
1430 void Position::do_null_move(StateInfo& backupSt) {
1433 assert(!in_check());
1435 // Back up the information necessary to undo the null move to the supplied
1436 // StateInfo object.
1437 // Note that differently from normal case here backupSt is actually used as
1438 // a backup storage not as a new state to be used.
1439 backupSt.key = st->key;
1440 backupSt.epSquare = st->epSquare;
1441 backupSt.value = st->value;
1442 backupSt.previous = st->previous;
1443 backupSt.pliesFromNull = st->pliesFromNull;
1444 st->previous = &backupSt;
1446 // Save the current key to the history[] array, in order to be able to
1447 // detect repetition draws.
1448 history[st->gamePly++] = st->key;
1450 // Update the necessary information
1451 if (st->epSquare != SQ_NONE)
1452 st->key ^= zobEp[st->epSquare];
1454 st->key ^= zobSideToMove;
1455 prefetch((char*)TT.first_entry(st->key));
1457 sideToMove = opposite_color(sideToMove);
1458 st->epSquare = SQ_NONE;
1460 st->pliesFromNull = 0;
1461 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1465 /// Position::undo_null_move() unmakes a "null move".
1467 void Position::undo_null_move() {
1470 assert(!in_check());
1472 // Restore information from the our backup StateInfo object
1473 StateInfo* backupSt = st->previous;
1474 st->key = backupSt->key;
1475 st->epSquare = backupSt->epSquare;
1476 st->value = backupSt->value;
1477 st->previous = backupSt->previous;
1478 st->pliesFromNull = backupSt->pliesFromNull;
1480 // Update the necessary information
1481 sideToMove = opposite_color(sideToMove);
1487 /// Position::see() is a static exchange evaluator: It tries to estimate the
1488 /// material gain or loss resulting from a move. There are three versions of
1489 /// this function: One which takes a destination square as input, one takes a
1490 /// move, and one which takes a 'from' and a 'to' square. The function does
1491 /// not yet understand promotions captures.
1493 int Position::see(Move m) const {
1495 assert(move_is_ok(m));
1496 return see(move_from(m), move_to(m));
1499 int Position::see_sign(Move m) const {
1501 assert(move_is_ok(m));
1503 Square from = move_from(m);
1504 Square to = move_to(m);
1506 // Early return if SEE cannot be negative because captured piece value
1507 // is not less then capturing one. Note that king moves always return
1508 // here because king midgame value is set to 0.
1509 if (midgame_value_of_piece_on(to) >= midgame_value_of_piece_on(from))
1512 return see(from, to);
1515 int Position::see(Square from, Square to) const {
1517 Bitboard occupied, attackers, stmAttackers, b;
1518 int swapList[32], slIndex = 1;
1519 PieceType capturedType, pt;
1522 assert(square_is_ok(from));
1523 assert(square_is_ok(to));
1525 capturedType = type_of_piece_on(to);
1527 // King cannot be recaptured
1528 if (capturedType == KING)
1529 return seeValues[capturedType];
1531 occupied = occupied_squares();
1533 // Handle en passant moves
1534 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1536 Square capQq = (side_to_move() == WHITE ? to - DELTA_N : to - DELTA_S);
1538 assert(capturedType == PIECE_TYPE_NONE);
1539 assert(type_of_piece_on(capQq) == PAWN);
1541 // Remove the captured pawn
1542 clear_bit(&occupied, capQq);
1543 capturedType = PAWN;
1546 // Find all attackers to the destination square, with the moving piece
1547 // removed, but possibly an X-ray attacker added behind it.
1548 clear_bit(&occupied, from);
1549 attackers = (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1550 | (bishop_attacks_bb(to, occupied)& pieces(BISHOP, QUEEN))
1551 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1552 | (attacks_from<KING>(to) & pieces(KING))
1553 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1554 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1556 // If the opponent has no attackers we are finished
1557 stm = opposite_color(color_of_piece_on(from));
1558 stmAttackers = attackers & pieces_of_color(stm);
1560 return seeValues[capturedType];
1562 // The destination square is defended, which makes things rather more
1563 // difficult to compute. We proceed by building up a "swap list" containing
1564 // the material gain or loss at each stop in a sequence of captures to the
1565 // destination square, where the sides alternately capture, and always
1566 // capture with the least valuable piece. After each capture, we look for
1567 // new X-ray attacks from behind the capturing piece.
1568 swapList[0] = seeValues[capturedType];
1569 capturedType = type_of_piece_on(from);
1572 // Locate the least valuable attacker for the side to move. The loop
1573 // below looks like it is potentially infinite, but it isn't. We know
1574 // that the side to move still has at least one attacker left.
1575 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1578 // Remove the attacker we just found from the 'occupied' bitboard,
1579 // and scan for new X-ray attacks behind the attacker.
1580 b = stmAttackers & pieces(pt);
1581 occupied ^= (b & (~b + 1));
1582 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1583 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1585 attackers &= occupied; // Cut out pieces we've already done
1587 // Add the new entry to the swap list
1588 assert(slIndex < 32);
1589 swapList[slIndex] = -swapList[slIndex - 1] + seeValues[capturedType];
1592 // Remember the value of the capturing piece, and change the side to
1593 // move before beginning the next iteration.
1595 stm = opposite_color(stm);
1596 stmAttackers = attackers & pieces_of_color(stm);
1598 // Stop before processing a king capture
1599 if (capturedType == KING && stmAttackers)
1601 assert(slIndex < 32);
1602 swapList[slIndex++] = QueenValueMidgame*10;
1605 } while (stmAttackers);
1607 // Having built the swap list, we negamax through it to find the best
1608 // achievable score from the point of view of the side to move.
1610 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1616 /// Position::clear() erases the position object to a pristine state, with an
1617 /// empty board, white to move, and no castling rights.
1619 void Position::clear() {
1622 memset(st, 0, sizeof(StateInfo));
1623 st->epSquare = SQ_NONE;
1624 startPosPlyCounter = 0;
1627 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1628 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1629 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1630 memset(index, 0, sizeof(int) * 64);
1632 for (int i = 0; i < 64; i++)
1633 board[i] = PIECE_NONE;
1635 for (int i = 0; i < 8; i++)
1636 for (int j = 0; j < 16; j++)
1637 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1639 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1640 castleRightsMask[sq] = ALL_CASTLES;
1643 initialKFile = FILE_E;
1644 initialKRFile = FILE_H;
1645 initialQRFile = FILE_A;
1649 /// Position::put_piece() puts a piece on the given square of the board,
1650 /// updating the board array, pieces list, bitboards, and piece counts.
1652 void Position::put_piece(Piece p, Square s) {
1654 Color c = color_of_piece(p);
1655 PieceType pt = type_of_piece(p);
1658 index[s] = pieceCount[c][pt]++;
1659 pieceList[c][pt][index[s]] = s;
1661 set_bit(&(byTypeBB[pt]), s);
1662 set_bit(&(byColorBB[c]), s);
1663 set_bit(&(byTypeBB[0]), s); // HACK: byTypeBB[0] contains all occupied squares.
1667 /// Position::compute_key() computes the hash key of the position. The hash
1668 /// key is usually updated incrementally as moves are made and unmade, the
1669 /// compute_key() function is only used when a new position is set up, and
1670 /// to verify the correctness of the hash key when running in debug mode.
1672 Key Position::compute_key() const {
1674 Key result = zobCastle[st->castleRights];
1676 for (Square s = SQ_A1; s <= SQ_H8; s++)
1677 if (square_is_occupied(s))
1678 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1680 if (ep_square() != SQ_NONE)
1681 result ^= zobEp[ep_square()];
1683 if (side_to_move() == BLACK)
1684 result ^= zobSideToMove;
1690 /// Position::compute_pawn_key() computes the hash key of the position. The
1691 /// hash key is usually updated incrementally as moves are made and unmade,
1692 /// the compute_pawn_key() function is only used when a new position is set
1693 /// up, and to verify the correctness of the pawn hash key when running in
1696 Key Position::compute_pawn_key() const {
1701 for (Color c = WHITE; c <= BLACK; c++)
1703 b = pieces(PAWN, c);
1705 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1711 /// Position::compute_material_key() computes the hash key of the position.
1712 /// The hash key is usually updated incrementally as moves are made and unmade,
1713 /// the compute_material_key() function is only used when a new position is set
1714 /// up, and to verify the correctness of the material hash key when running in
1717 Key Position::compute_material_key() const {
1722 for (Color c = WHITE; c <= BLACK; c++)
1723 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1725 count = piece_count(c, pt);
1726 for (int i = 0; i < count; i++)
1727 result ^= zobrist[c][pt][i];
1733 /// Position::compute_value() compute the incremental scores for the middle
1734 /// game and the endgame. These functions are used to initialize the incremental
1735 /// scores when a new position is set up, and to verify that the scores are correctly
1736 /// updated by do_move and undo_move when the program is running in debug mode.
1737 Score Position::compute_value() const {
1740 Score result = SCORE_ZERO;
1742 for (Color c = WHITE; c <= BLACK; c++)
1743 for (PieceType pt = PAWN; pt <= KING; pt++)
1747 result += pst(c, pt, pop_1st_bit(&b));
1750 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1755 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1756 /// game material value for the given side. Material values are updated
1757 /// incrementally during the search, this function is only used while
1758 /// initializing a new Position object.
1760 Value Position::compute_non_pawn_material(Color c) const {
1762 Value result = VALUE_ZERO;
1764 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1765 result += piece_count(c, pt) * PieceValueMidgame[pt];
1771 /// Position::is_draw() tests whether the position is drawn by material,
1772 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1773 /// must be done by the search.
1775 bool Position::is_draw() const {
1777 // Draw by material?
1779 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1782 // Draw by the 50 moves rule?
1783 if (st->rule50 > 99 && !is_mate())
1786 // Draw by repetition?
1787 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1788 if (history[st->gamePly - i] == st->key)
1795 /// Position::is_mate() returns true or false depending on whether the
1796 /// side to move is checkmated.
1798 bool Position::is_mate() const {
1800 MoveStack moves[MAX_MOVES];
1801 return in_check() && generate<MV_LEGAL>(*this, moves) == moves;
1805 /// Position::init_zobrist() is a static member function which initializes at
1806 /// startup the various arrays used to compute hash keys.
1808 void Position::init_zobrist() {
1813 for (i = 0; i < 2; i++) for (j = 0; j < 8; j++) for (k = 0; k < 64; k++)
1814 zobrist[i][j][k] = rk.rand<Key>();
1816 for (i = 0; i < 64; i++)
1817 zobEp[i] = rk.rand<Key>();
1819 for (i = 0; i < 16; i++)
1820 zobCastle[i] = rk.rand<Key>();
1822 zobSideToMove = rk.rand<Key>();
1823 zobExclusion = rk.rand<Key>();
1827 /// Position::init_piece_square_tables() initializes the piece square tables.
1828 /// This is a two-step operation: First, the white halves of the tables are
1829 /// copied from the MgPST[][] and EgPST[][] arrays. Second, the black halves
1830 /// of the tables are initialized by mirroring and changing the sign of the
1831 /// corresponding white scores.
1833 void Position::init_piece_square_tables() {
1835 for (Square s = SQ_A1; s <= SQ_H8; s++)
1836 for (Piece p = WP; p <= WK; p++)
1837 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1839 for (Square s = SQ_A1; s <= SQ_H8; s++)
1840 for (Piece p = BP; p <= BK; p++)
1841 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1845 /// Position::flip() flips position with the white and black sides reversed. This
1846 /// is only useful for debugging especially for finding evaluation symmetry bugs.
1848 void Position::flip() {
1852 // Make a copy of current position before to start changing
1853 const Position pos(*this, threadID);
1856 threadID = pos.thread();
1859 for (Square s = SQ_A1; s <= SQ_H8; s++)
1860 if (!pos.square_is_empty(s))
1861 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1864 sideToMove = opposite_color(pos.side_to_move());
1867 if (pos.can_castle_kingside(WHITE)) do_allow_oo(BLACK);
1868 if (pos.can_castle_queenside(WHITE)) do_allow_ooo(BLACK);
1869 if (pos.can_castle_kingside(BLACK)) do_allow_oo(WHITE);
1870 if (pos.can_castle_queenside(BLACK)) do_allow_ooo(WHITE);
1872 initialKFile = pos.initialKFile;
1873 initialKRFile = pos.initialKRFile;
1874 initialQRFile = pos.initialQRFile;
1876 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1877 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1878 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1879 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1880 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1881 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1883 // En passant square
1884 if (pos.st->epSquare != SQ_NONE)
1885 st->epSquare = flip_square(pos.st->epSquare);
1891 st->key = compute_key();
1892 st->pawnKey = compute_pawn_key();
1893 st->materialKey = compute_material_key();
1895 // Incremental scores
1896 st->value = compute_value();
1899 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1900 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1906 /// Position::is_ok() performs some consitency checks for the position object.
1907 /// This is meant to be helpful when debugging.
1909 bool Position::is_ok(int* failedStep) const {
1911 // What features of the position should be verified?
1912 const bool debugAll = false;
1914 const bool debugBitboards = debugAll || false;
1915 const bool debugKingCount = debugAll || false;
1916 const bool debugKingCapture = debugAll || false;
1917 const bool debugCheckerCount = debugAll || false;
1918 const bool debugKey = debugAll || false;
1919 const bool debugMaterialKey = debugAll || false;
1920 const bool debugPawnKey = debugAll || false;
1921 const bool debugIncrementalEval = debugAll || false;
1922 const bool debugNonPawnMaterial = debugAll || false;
1923 const bool debugPieceCounts = debugAll || false;
1924 const bool debugPieceList = debugAll || false;
1925 const bool debugCastleSquares = debugAll || false;
1927 if (failedStep) *failedStep = 1;
1930 if (!color_is_ok(side_to_move()))
1933 // Are the king squares in the position correct?
1934 if (failedStep) (*failedStep)++;
1935 if (piece_on(king_square(WHITE)) != WK)
1938 if (failedStep) (*failedStep)++;
1939 if (piece_on(king_square(BLACK)) != BK)
1943 if (failedStep) (*failedStep)++;
1944 if (!file_is_ok(initialKRFile))
1947 if (!file_is_ok(initialQRFile))
1950 // Do both sides have exactly one king?
1951 if (failedStep) (*failedStep)++;
1954 int kingCount[2] = {0, 0};
1955 for (Square s = SQ_A1; s <= SQ_H8; s++)
1956 if (type_of_piece_on(s) == KING)
1957 kingCount[color_of_piece_on(s)]++;
1959 if (kingCount[0] != 1 || kingCount[1] != 1)
1963 // Can the side to move capture the opponent's king?
1964 if (failedStep) (*failedStep)++;
1965 if (debugKingCapture)
1967 Color us = side_to_move();
1968 Color them = opposite_color(us);
1969 Square ksq = king_square(them);
1970 if (attackers_to(ksq) & pieces_of_color(us))
1974 // Is there more than 2 checkers?
1975 if (failedStep) (*failedStep)++;
1976 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1980 if (failedStep) (*failedStep)++;
1983 // The intersection of the white and black pieces must be empty
1984 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1987 // The union of the white and black pieces must be equal to all
1989 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1992 // Separate piece type bitboards must have empty intersections
1993 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1994 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1995 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1999 // En passant square OK?
2000 if (failedStep) (*failedStep)++;
2001 if (ep_square() != SQ_NONE)
2003 // The en passant square must be on rank 6, from the point of view of the
2005 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2010 if (failedStep) (*failedStep)++;
2011 if (debugKey && st->key != compute_key())
2014 // Pawn hash key OK?
2015 if (failedStep) (*failedStep)++;
2016 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2019 // Material hash key OK?
2020 if (failedStep) (*failedStep)++;
2021 if (debugMaterialKey && st->materialKey != compute_material_key())
2024 // Incremental eval OK?
2025 if (failedStep) (*failedStep)++;
2026 if (debugIncrementalEval && st->value != compute_value())
2029 // Non-pawn material OK?
2030 if (failedStep) (*failedStep)++;
2031 if (debugNonPawnMaterial)
2033 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2036 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2041 if (failedStep) (*failedStep)++;
2042 if (debugPieceCounts)
2043 for (Color c = WHITE; c <= BLACK; c++)
2044 for (PieceType pt = PAWN; pt <= KING; pt++)
2045 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
2048 if (failedStep) (*failedStep)++;
2050 for (Color c = WHITE; c <= BLACK; c++)
2051 for (PieceType pt = PAWN; pt <= KING; pt++)
2052 for (int i = 0; i < pieceCount[c][pt]; i++)
2054 if (piece_on(piece_list(c, pt, i)) != make_piece(c, pt))
2057 if (index[piece_list(c, pt, i)] != i)
2061 if (failedStep) (*failedStep)++;
2062 if (debugCastleSquares)
2064 for (Color c = WHITE; c <= BLACK; c++)
2066 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != make_piece(c, ROOK))
2069 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != make_piece(c, ROOK))
2072 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
2074 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
2076 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
2078 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
2082 if (failedStep) *failedStep = 0;